ST STM32L4+ Series Reference Manual page 1098

AES hardware accelerator (AES)
Cipher block chaining (CBC) mode
Legend
In CBC mode the output of each block chains with the input of the following block. To make
each message unique, an initialization vector is used during the first block processing.
Note: For decryption, a special key scheduling is required before processing the first block.
1098/2301
Figure 254. CBC encryption and decryption principle
Plaintext block 1
initialization
vector
key
Encrypt
Ciphertext block 1
Plaintext block 1
initialization
vector
key
input
output
key
scheduling
Ciphertext block 1
Encryption
Plaintext block 2
key
Encrypt
Ciphertext block 2
Decryption
Plaintext block 2
key
Decrypt Decrypt
Ciphertext block 2
RM0432 Rev 6
RM0432
Plaintext block 3
key
Encrypt
Ciphertext block 3
Plaintext block 3
key
Decrypt
Ciphertext block 3
MSv42141V1